Establishing the presence and state of organic matter, including its possible biosignatures, in martian materials has been an elusive quest, despite limited reports of the existence of organic matter on Mars. We report the in situ detection of organic matter preserved in lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds released at high temperatures (500° to 820°C), were directly detected by evolved gas analysis. Thiophenes were also observed by gas chromatography–mass spectrometry. Their presence suggests that sulfurization aided organic matter preservation. At least 50 nanomoles of organic carbon persists, probably as macromolecules containing 5% carbon as organic sulfur molecules.

1. PLANETARY SCIENCE
Organic matter preserved in
3-billion-year-old mudstones
at Gale crater, Mars
Jennifer L. Eigenbrode1
*, Roger E. Summons2
, Andrew Steele3
, Caroline Freissinet1
†,
Maëva Millan4
‡, Rafael Navarro-González5
, Brad Sutter6,7
, Amy C. McAdam1
,
Heather B. Franz1
, Daniel P. Glavin1
, Paul D. Archer Jr.6
, Paul R. Mahaffy1
,
Pamela G. Conrad1
§, Joel A. Hurowitz8
, John P. Grotzinger9
, Sanjeev Gupta10
,
Doug W. Ming7
, Dawn Y. Sumner11
, Cyril Szopa4
, Charles Malespin1
,
Arnaud Buch12
, Patrice Coll13
Establishing the presence and state of organic matter, including its possible biosignatures,
in martian materials has been an elusive quest, despite limited reports of the existence
of organic matter on Mars. We report the in situ detection of organic matter preserved in
lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump
Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity
rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds
released at high temperatures (500° to 820°C), were directly detected by evolved gas
analysis. Thiophenes were also observed by gas chromatography–mass spectrometry.Their
presence suggests that sulfurization aided organic matter preservation.
At least 50 nanomoles of organic carbon persists, probably as macromolecules containing
5% carbon as organic sulfur molecules.
O
rganic matter preservation is central to un-
derstanding biological potential on Mars
through time. Whether it holds a record
of ancient life, is the food for extant life, or
has existed in the absence of life, organic
matter in martian materials holds chemical clues
to planetary conditions and processes.
Prior reports of organic matter indigenous to
martian sediments include 150 to 300 parts per
billion(ppb)ofchlorobenzene,withlesseramounts
of C2 to C4 dichloroalkanes, detected in Sheepbed
mudstone upon heating to <400°C by the Sample
Analysis at Mars (SAM) instrument suite of the
Mars Science Laboratory (MSL) mission (1). Mar-
tian organic carbon may have also contributed to
CO and CO2 pyrolysis and combustion products
evolved below 700°C from various sediments by
SAM (2, 3). Chloromethanes detected in Viking’s
pyrolysis gas chromatography–mass spectrometry
(GC-MS) analysis of martian regolith have been
reinterpreted as having a martian origin (4). Ad-
ditionally, indigenous organic matter in martian
meteorites [e.g., (5)] is related to a deep igneous
domain excavated by impact events. Although
these reports indicate the presence of martian
organic matter, they do not constrain our under-
standing of ancient organic matter in sediments.
Exploration of the lowermost exposed sedi-
mentary rocks at the base of Aeolis Mons in Gale
crater by the Curiosity rover has led to the discov-
ery of a finely laminated mudstone succession,
the Murray formation, that is interpreted to re-
cord deposition in a long-lived ancient circum-
neutral to alkaline lake fed by a fluviodeltaic
sedimentary system (6–8). Mudstones are com-
posed of basaltic minerals mixed with phyllo-
silicate, sulfate, iron oxide, and x-ray amorphous
components (7). The ~3.5-billion-year-old Gale
lake environment(s) are expected to have been
ideal settings for concentrating and preserv-
ing organic matter (9).
Drilled samples delivered to SAM were heated
at ~35°C/min to ~860°C. Evolved gas analysis
(EGA) continuously and directly measured bulk
gas composition during heating with the mass
spectrometer. A portion of the evolved gas from
the same sample was trapped and analyzed by
GC-MS for molecular identifications (10, 11). Here
we report the analysis of gases evolved at high
temperatures (>500°C) from the Mojave and Con-
fidence Hills sites. We also make comparisons
with Sheepbed and other Murray mudstones.
Figure 1, A and B, shows mass-to-charge ratio
(m/z) profiles for the release of organic sulfur
compounds from Mojave samples. The profiles,
which are indicative of particular compounds or
fragments of similar structures, reached their
peak between 500° and 820°C, consistent with
the presence of thiophene (C4H4S), 2- and 3-
methylthiophenes (C5H6S), methanethiol (CH4S),
and dimethylsulfide (C2H6S). The presence of
benzothiophene (C8H6S), a bicyclic thiophene
that usually co-occurs with thiophenes, is also
suggested by a weak peak in both Mojave (Fig.
1A) and Confidence Hills (fig. S1F) EGA data.
Other volatiles—carbonyl sulfide (COS), CS2,
H2S, SO2, O2, CO, and CO2 but not H2—evolved
concurrently (Fig. 1, C to E). A similar release of
organic sulfur compounds and related volatiles
was observed for Confidence Hills (fig. S1).
Other, nonthiophenic, aromatic compounds
were also detected in EGA of Mojave (Fig. 2B)
and Confidence Hills (fig. S2F) samples. The tem-
peratures of peak release and the correspond-
ing representative molecular groups are ~800°C
for benzene (C6H6) and ~750°C for toluene (or
tropylium ion C7H7
+
), with two peaks at 625° and
790° to 820°C for alkylbenzenes (C8H9 or ben-
zoate ion C7H5O−
) and possible chlorobenzene
(C6H5Cl) (supplementary text). A peak near de-
tection limits in the Mojave data suggests that
naphthalene (C10H8) may also be present, assum-
ing that the Confidence Hills blank (fig. S2E) is
representative of noise levels.
EGA mass profiles for m/z 15, 26, 27, 29c [where
“c” indicates a profile correction to remove con-
tributions from other volatiles (11)], 30, 41 to 43,
55 to 57, and 69 to 71 from Mojave (Fig. 2A) and
Confidence Hills (fig. S2B) samples are consistent
with a 550° to 820°C evolution of aliphatic com-
pound products composed of C1 to C5 chains or
their branched moieties. Correlation and relative
intensities of peaks suggest molecular structures
that differ by single carbon additions (–CH–,
–CH2–, and –CH3 additions), which are charac-
teristic of an array of aliphatic fragments from
larger molecules (12) and commonly observed in
high-temperature pyrolysis products of terres-
trial kerogens and coals (13) and carbonaceous
chondrites (14). Some structures may contain
N- and O-bearing groups, such as amides or car-
boxyl or carbonyl groups, but these cannot be
clearly identified in EGA because mass spectra
are not resolvable in EGA and other molecules
share the diagnostic m/z values.
Three temperatures or ranges characterize the
peaks of the aliphatic compound signals in the
Mojave data (Fig. 2A): 625°C (square), 750°C
(circles), and 790° to 820°C (triangles). Imme-
diately preceding the 750°C peak set is a nota-
ble O2 release from sulfate decomposition (3),
with an increase in CO2 (Fig. 1E) suggesting that
combustion limited to the most ignitable vola-
tiles (12) occurred in parallel with pyrolysis. It
is also possible that portions of the CO2 and CO
(Fig. 2A) were derived from the decarboxylation
(2, 3) and decarbonylation of larger organic com-
pounds, which have been observed for Murchison
macromolecular isolates (15). The same three
peaks are present but less discernable in Confi-
dence Hills data, where the 750°C O2 peak is
lower, suggesting that combustion was less influ-
ential on hydrocarbon evolution (fig. S1 and S2).
Abundance estimates for thiophenes, C1 and
C2 sulfur, and aromatic and aliphatic compounds
in Mojave and Confidence Hills samples are in the
nanomolar C range (Table 1) (11). The total organic
carbon (TOC) abundance in these samples (10 to
100 nmol of C) reflects only the portion detected in
EGA and does not account for any char remaining
in the samples after heating. Calculated TOC
abundances are considered lower limits for the
actual amounts of organic carbon in the samples.
Organic sulfur and aromatic and aliphatic
components evolve between 550° and 820°C
and share peak maxima (noted by symbols in
Figs. 1 and 2 and figs. S1 and S2). This match-
ing indicates the presence of diverse molecular
structures in organic matter of the Mojave and
Confidence Hills samples. Peaks for aromatic or
thiophenic volatiles in the Sheepbed and other
RESEARCH
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2. Murray mudstones (fig. S1 to S6) are weaker and
less defined and have inconsistent temperatures,
despite a clear indication of aliphatic compound
presence. Thiophenic and aromatic compound
abundances for these mudstones are less than
50%, as observed for Mojave and Confidence
Hills samples (table S1). In the Cumberland sam-
ple of the Sheepbed mudstone, thiophene abun-
dances are equivalent to or less than values for
blanks, indicating their absence.
GC-MS analysis of the 226° to 860°C cut of
gases released from Mojave (Fig. 3) confirms the
presence of thiophene, 2-methylthiophene, and
3-methylthiophene. Dimethylsulfide was observed
in all GC-MS analyses (table S2). The abundance
of thiophenes detected in Mojave by GC-MS is
20 (±5) pmol of molecules (table S2), which is
equivalent to ~100 pmol of C, indicating 10 times
less thiophenic C than in EGA. The difference
reflects a combination of contributions from
other unknown molecules [e.g., for the m/z 84c
profile (Fig. 1A), other thiophenic or sulfur aro-
matic compounds and C6H12 fragments from
aliphatic chains with fewer than six carbons, and
for the m/z 97 profile, C7H13 fragments or HSO4
−
cleaved from aliphatic and aromatic sulfates]
(12, 16) in EGA, leading to inflation of calculated
EGA abundances; incomplete hydrocarbon trap-
ping by the SAM hydrocarbon and injection traps
of the GC system because of interference from
other volatiles; and incomplete release from
flash heating of the injection trap.
GC-MS confirmations of molecular identities
assigned to EGA aromatic signals are limited.
Benzene, alkylbenzenes, naphthalene, and chlo-
robenzene are observed in GC-MS data for Mo-
jave and Confidence Hills, but molecules from
the GC instrument background contribute to
these signals, and the GC detections likely in-
clude contributions evolved at low temperatures
(<500°C) because of the broad GC cut (table S2).
Sample-to-sample carryover is also known to
affect low GC-MS signals (1). Together, these
issues make distinction among small amounts
of high-temperature, sample-derived aromatic
molecules difficult. Moreover, because peaks in
EGA profiles reflect the sum of hydrocarbon
fragments with a characteristic structure that
are contributed by numerous, low-abundance
pyrolysis products, signals of individual mole-
cules can be significantly lower in GC-MS. Such
diverse molecular contributions are consistent
with the complex chemistry of meteoritic and geo-
logical organic matter and the interactions that
occur during pyrolysis of sediments (12). The
Mojave and Confidence Hills GC-MS data do not
andarenotexpectedtoprovide unequivocalmolec-
ular identifications for the small amounts of
aromatic compounds indicated by the EGA data.
Aliphatic compound identifications in GC-MS
data for Mojave and Confidence Hills do not
reflect those observed in EGA. Generally, the
strongest m/z values in mass spectra of aliphatic
compounds are from the C2 to C5 fragments of
parent molecules with larger carbon structures.
Thus, the disparity between EGA and GC-MS
data is largely attributable to C2 to C5 fragment
contributions from a large molecular pool in
EGA, which renders identification of any one
molecule below detection limits by GC-MS, as
previously described for aromatic compounds.
The SAM EGA instrument background is not
the source of the molecular diversity observed at
high temperatures (supplementary text). Sample
signals are significantly greater than blanks. Lab-
oratory tests demonstrate that in the presence
of silicates and perchlorates, instrument back-
ground has little effect on signals above 550°C
(fig. S7). Other possible but unlikely contamina-
tion sources cannot account for the temperature
breadth and the molecular diversity observed.
Lastly, C5 structures suggested by m/z profiles
cannot be explained by SAM’s instrument back-
ground, which is limited to C1 to C4 backbones.
The diversity, composition, and temperatures
of coevolving volatiles observed in the Mojave
and Confidence Hills analyses above 500°C are
consistent with the pyrolysis of geologically re-
fractory organic macromolecules that are typ-
ically found in carbonaceous chondrites (14, 15),
kerogens (17), and coals (18, 19). The more stable
these macromolecules are, the higher the tem-
perature needed to thermally cleave fragments
from them. Pyrolysis of organic matter-laden sed-
iments with co-occurring inorganic materials
that also decompose or act as catalysts can re-
sult in a complex array of chemical reactions
during heating, including sulfurization, addi-
tion, cyclization, and condensation (Diels-Alder
Eigenbrode et al., Science 360, 1096–1101 (2018) 8 June 2018 2 of 5
Fig. 1. Mojave EGA
profiles for volatiles.
Profiles for thiophenes
(A), thiols and sulfides
(B and C), other volatiles
(D), and O2 and CO2 (E) are
shown. The identity of the
volatile, the m/z, and the
scaling factor are listed for
each profile. Profiles within
panels are multiplied by
scaling factors. Symbols
mark correlations between
panels in peak maxima within
an error of ±25°C due to
signal smoothing: squares,
625°C; circles, 750°C; and
triangles, 790 to 820°C.
Axes and the placement of
symbols relative to the
temperature are the same in
Fig. 2 and figs. S1 to S6. The
x axis is scaled linearly
relative to the run time, and
the corresponding sample
temperature is shown. The
y-axis scale bar in counts per
second (cps) is for all panels.
Profiles in (A) are shifted
along the y axis to show
peaks clearly. In m/z values,
“c” indicates corrections to
profiles to remove contribu-
tions from other volatiles
(11). i, isotopologue.
1
Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. 2
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of
Technology, Cambridge, MA 02139, USA. 3
Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA. 4
Laboratoire Atmosphères, Milieux, Observations Spatiales,
Université Pierre et Marie Curie, Université Versailles Saint-Quentin and CNRS, Paris, France. 5
Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Ciudad
Universitaria, Cuidad de México 04510, México. 6
Jacobs Technology, Houston, TX 77058, USA. 7
Astromaterials Research and Exploration Science Division, NASA Johnson Space Center,
Houston, TX 77058, USA. 8
Department of Geosciences, Stony Brook University, Stony Brook, NY 11794, USA. 9
Division of Geological and Planetary Sciences, California Institute of
Technology, Pasadena, CA 91125, USA. 10
Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK. 11
Department of Earth and Planetary Sciences,
University of California, Davis, CA 95616, USA. 12
Laboratoire Génie des Procédés et Matériaux, Centrale Supélec, Gif-sur-Yvette, France. 13
Laboratoire Inter-Universitaire des Systèmes
Atmosphériques, Université Paris-Est Créteil, Université Paris Diderot and CNRS, Créteil, France.
*Corresponding author. Email: jennifer.l.eigenbrode@nasa.gov †Present address: Laboratoire Atmosphères, Milieux, Observations Spatiales, Institut Pierre Simon Laplace, CNRS, Guyancourt, France.
‡Present address: Department of Biology, Georgetown University, Washington, DC 20057, USA. §Present address: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
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3. type) reactions that may produce cyclic struc-
tures (thiophenes and other aromatics). Sufficient
He flow mitigates these secondary reactions. In
spite of this complexity, larger molecular frag-
ments can maintain structural information re-
garding the parent organic matter (12, 13). In
Mojave, CO, COS, CS2, CH4S, and C2H6S likely
reflect cleavage directly from the precursor or-
ganic structures and reaction products. Sim-
ilarly, CO2, H2S, H2, and H2O may be derived
partly from organic matter in addition to min-
eral decomposition (3, 20). However, under
SAM oven conditions at high temperatures and
low pressure under flowing He, entropic factors
govern reactions (12, 21, 22), and the forma-
tion of thiophenic and other aromatic volatiles in
the oven is not favored. This conclusion is sup-
ported by EGA blank analyses that indicate
the absence of cyclic structures (fig. S2) despite
available reactants from the background or-
ganic molecules (fig. S7) and by the absence of
thiophenes in EGA data for the sulfide-bearing
Cumberland sample of the Sheepbed mudstone,
indicating that no cyclization occurred (table
S1). Thus, the thiophenic and aromatic volatiles
likely reflect compounds directly released from
organic matter in the Murray mudstones. It is
very plausible that aliphatics and some portion
of the C1 and C2 sulfur compounds also reflect
the in situ sample chemistry. Even if some por-
tion of these compounds are not direct pyroly-
sis products from sediments, their carbon must
largely be derived from organic matter indige-
nous to martian sediments.
The weaker and less diverse organic signals
of the Sheepbed and other Murray mudstones
indicate that the sediments had less organic in-
put at the time of deposition or that the organic
inputs were more substantially degraded over
geological time. Organic materials in the lacus-
trine mudstones at Yellowknife Bay and in the
lower Mount Sharp group strata have survived
multiple aqueous diagenetic events (6–8), though
the number and extent of these are difficult to
constrain. Further, direct and indirect reactions
induced by ionizing cosmic rays degrade organic
matter (23), and SAM measurements of noble
gas isotopes in the Sheepbed mudstones indi-
cate that the sediments have been irradiated for
~80 million years, implying substantial degra-
dation (24). It is possible that the Murray mud-
stones experienced less exposure.
WithinthelowerMurraymudstonesatPahrump
Hills, sulfide minerals were likely alteredtojarosite
(1 to 3% in Mojave and Confidence Hills) by acidic
diagenetic fluids (pH 2 to 6) ~2.1 billion years ago
(25), though it is unclear whether these fluids
were localized to sediment grains (8) or were more
pervasive in the strata, leaching mafic minerals
of metals and increasing in pH as they passed
downward through the section (7). In either case,
the exposure must have been limited in time and
space, as pH-sensitive minerals such as apatite
and olivine persist. Acidic fluids can effectively
oxidize exposed organics; however, acidic diagen-
esis in the lower Murray may have had a small
effect on organics, as it did on pH-sensitive min-
erals. If these fluids moved downward through
the Pahrump Hills section as proposed by Rampe
et al. (7), Confidence Hills and Mojave would
have been exposed to only mildly acidic fluids
(pH 6), resulting in milder organic degradation
than that of overlying Murray mudstones. Alter-
natively, variations in organic matter abundance
and composition in Murray mudstones may re-
flect geological inputs from transported detri-
tus that was already in a refractory state, which
would support the survival of organic detritus
exposed to varied lake redox conditions (8). Ul-
timately, the fate of organic matter is determined
by both degradation and preservation mecha-
nisms. Both are likely important to the mudstones
in Gale crater. By what preservation mechanisms
did the martian organic matter survive?
Macromoleculesontheirownareself-preserving
because surface organics shield interior organics
from oxidation and stabilize the bulk organic mass
(26). Ancient biomacromolecules deposited in lake
sediments may have been transformed into geo-
macromolecules (kerogen) over time. Other possi-
ble sources of recalcitrant macromolecules include
interplanetary dust particles (IDPs) (27) and abi-
otic organic materials from igneous rocks (5). In
an effort to better constrain the composition and
possible origin of organic matter in the mud-
stones, we conducted SAM test bed EGA of the
Murchison meteorite, a proxy for IDP composi-
tion, and laboratory EGA of the Tissint martian
meteorite, which hosts igneous rock–related or-
ganics. Both show the evolution of C1-C2 sulfur
volatiles and aliphatic, aromatic, and thiophenic
pyrolysis products during EGA above 500°C (fig.
S9 and S10), but the profiles related to these
molecular groups are distinctive for each sample
type. These results are consistent with the known
Eigenbrode et al., Science 360, 1096–1101 (2018) 8 June 2018 3 of 5
Fig. 2. Mojave EGA
profiles for aliphatic and
aromatic compounds.
CO and CO2 profiles are
included with aliphatic
profiles in (A). Profiles in
(A) are grouped by carbon
number and shifted
along the y axis for clarity.
Profiles for aromatic
compounds in (B) are
similarly shifted. Plotting
details are as described
in the legend to Fig. 1 (11).
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4. presence of refractory organic matter in each
meteorite but indicate differences in the organic
chemistry and mineral associations of the mete-
orites. The supplemental EGAs do not provide
constraints on organic matter origin. However,
they do support the interpretation that the mud-
stones host refractory organic matter that is most
likely macromolecular.
Minerals can further aid preservation by sev-
eral mechanisms: occlusion by minerals, organic-
mineral interactions (e.g., organic binding to
phyllosilicate and Al-Fe oxyhydroxide surfaces),
and the establishment of chemically reducing
microenvironments that host organics (28). If
organic matter entering sediments was labile,
such as autochthonous biomolecules (e.g., car-
bohydrates, amino acids, and fatty acids), then
reactions with mineral surfaces or sedimentary
chemicals would have been favored. Phyllosilicate,
iron oxyhydroxide, and amorphous materials are
prevalent in all of the studied mudstones (7, 8).
Further, iron sulfides detected in the Sheepbed
mudstone (29) and suspected in the original
Murray mudstone detritus (7, 8) may have aided
organic matter preservation by providing an
additional oxygen sink during diagenesis.
Reduced permeability limits the exposure of
organics to migrating fluids and gas. Permeabil-
ity is generally reduced by abundant fine-grained
sediments and precipitates (e.g., sulfate cement,
vein fill, and nodules). All mudstones studied
exhibit indications of groundwater alteration
(6–8, 30); however, the timing of cementation
and postdepositional aqueous alteration is not
well constrained, so the extent of organic expo-
sure to these fluids is unknown.
Macromolecules, mineral interactions, and
permeability factors were all likely contributors
to organic matter preservation in the Murray
mudstone, but sulfurization of organic molecules
was probably the principal preservation mecha-
nism responsible for the distinct record in Mojave
and Confidence Hills given the presence of 3 to
10 times as much thiophenic and total organic
sulfur in these samples as in the other mudstones
(tables S1 and S4). Natural vulcanization results
in an enhanced refractory state for organic mate-
rials. The addition of sulfur structurally links the
organic components into a macromolecular form
and provides an additional oxidative sink for deg-
radation reactions. On Earth, sulfurization en-
hances initial preservation while also imparting
long-term recalcitrance to structural transforma-
tions and oxidation, such as during acidic dia-
genesis. Sulfurization probably occurred during
early diagenesis in the presence of reduced sulfur
(HS−
or H2S) gas (31) more than 3 billion years
ago. The large sulfur isotopic fractionation ob-
served in the SO2 evolved via EGA from the
mudstones indicates that sulfide was transported
via hydrothermal groundwater to the Gale lake
basin (32). Alternatively, organic sulfur was na-
tive to the detritus deposited in the lake.
SAM’s molecular observations do not clearly
reveal the source of the organic matter in the
Murray formation. Biological, geological, and
meteoritic sources are all possible. Certainly, if
ancient life was the organic source, then despite
sulfur incorporation, the material has been al-
tered sufficiently, such as by diagenesis or ioniz-
ing radiation (23), to obscure original molecular
features more consistent with life (e.g., a greater
diversity of molecules or patterns of limited
structural variation within compound classes,
such as hydrocarbon chains), or an insufficient
amount of organic matter was deposited to allow
detection by pyrolysis–GC-MS.
Past habitability interpreted for the Sheepbed
lacustrine mudstones focused on chemolithoau-
totrophy (8, 30), but observations of geologically
refractory organic matter in Murray lacustrine
mudstones opens the door for past and present
habitability for heterotrophy as well. Organic
matter can directly or indirectly fuel both energy
and carbon metabolisms and in doing so can
support carbon cycling at the microbial commu-
nity level.
Eigenbrode et al., Science 360, 1096–1101 (2018) 8 June 2018 4 of 5
Fig. 3. Example of SAM GC-MS identification of S-containing pyrolysis
products compared with results from a high-fidelity SAM-like GC run
in the same manner but in the laboratory. (A) SAM GC-MS chromatograms
summing m/z 47 and 62 from 0 to 300 s for Cumberland7 of the Sheepbed
mudstone and a blank showing methanethiol and dimethylsulfide. (B) SAM
GC-MS chromatograms summing m/z 84, 97, and 98 from 300 to 1000 s
for Mojave and a blank showing the presence of thiophene, 2-methylthiophene,
and 3-methylthiophene. 2,5-Dimethylthiophene was not identifiable.
(C) Chromatograms from GC run in the laboratory. Chromatograms were
smoothed, and the off-nominal GC run from Mojave resulted in the 20-s
offset for the thiophene retention time as observed in (B) (11). The 2,2,2-
trifluoro-N-methyl-acetamide peak in (B) is a derivatization reaction
product that is part of the instrument background (11). GC-MS identifications
are based on both SAM and laboratory retention times (table S3)
compared to standards and mass spectra in a reference database (33).
Axis breaks denote a change in the x-axis scale.
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5. Our results suggest that it is likely that organic
matter from various sources may be widely dis-
tributed in the martian rock record. Even if life
was not a key contributor, meteoritic and igneous
or hydrothermal sources have a strong potential
to be broadly emplaced. Our detection of organic
matter at the martian surface, where ionizing and
oxidizing conditions are extreme, suggests that
better-preserved molecular records may be present
below the surface, where the effects of radiation
are small, or in materials exposed in the last sev-
eral thousand years.
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ACKNOWLEDGMENTS
We thank reviewers for their constructive comments, the MSL
and SAM teams for successful operations of SAM on Mars
and thoughtful science discussions, and K. Irikura for calculating
ionization cross sections. Funding: This work was funded
by NASA’s Mars Exploration Program. NASA’s MSL Participating
Scientist program supported J.L.E., R.E.S., and D.P.G. for this
effort. S.G. acknowledges funding from the UK Space Agency.
R.N.-G. was funded by the Universidad Nacional Autónoma
de México and the Consejo Nacional de Ciencia y Tecnología
de México. Author contributions: J.L.E. developed data
processing methods, calculated and interpreted EGA data, and
wrote most of the manuscript and supplementary materials.
R.E.S, A.S, B.S., and P.R.M. wrote sections of text on pyrolysis,
meteorites, geological context, and methods, respectively.
C.F., M.M., D.P.G., A.S., and C.S. calculated and interpreted
GC-MS data. M.M. performed SAM GC breadboard tests. H.B.F.,
P.D.A., and B.S. contributed to analysis of EGA data. R.N-G.
performed laboratory analyses necessary to understand the
SAM background. All authors participated in data acquisition,
discussion of results, and/or editing of the manuscript.
Competing interests: The authors declare no competing
financial interests. Data and materials availability: Reduced
data records (RDRs) from SAM flight experiments are archived
in the Planetary Data System (https://pds.nasa.gov) and are
identifiable by the sol or test identification (TID) numbers listed
in table S6. All processed data are available in the text or the
supplementary materials.
SUPPLEMENTARY MATERIALS
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Materials and Methods
Supplementary Text
Figs. S1 to S11
Tables S1 to S10
References (34–58)
4 January 2018; accepted 29 March 2018
10.1126/science.aas9185
Eigenbrode et al., Science 360, 1096–1101 (2018) 8 June 2018 5 of 5
Table 1. Organic carbon abundance estimates for EGA signals above 500°C. See table S1 for abundances of individual molecules and abundances in other
mudstones. Errors are propagated from integration uncertainty (30%, ±1s SD, n ≥ 3 analyses), smoothing error (5%, ±1s SD, n ≥ 3 analyses), and ionization
cross-section uncertainties (reported in the literature). The total for thiophenic compounds is the sum of thiophene and methyl thiophene abundances. The
total for other aromatic compounds is the sum of abundances of benzene, toluene, and benzoic acid (a proxy for benzoate ion or alkylbenzene contributions).
The total for aliphatic compounds is the sum of C1 to C3 alkanes and C2 to C5 alkenes determined from modeling. The total for C1 and C2 sulfur compounds
is the sum of methanethiol, dimethylsulfide, carbonyl sulfide, and carbon disulfide abundances (11).
Sample
Organic carbon abundance (nmol of C) in compound class(es)
Total organic carbon
(nmol of C)Thiophenic Aromatic Aliphatic
Thiophenic,
aromatic,
and aliphatic
C1 and C2
sulfur
Mojave 2.20 ± 0.93 6.99 ± 1.99 38.4 ± 5.63 47.61 ± 6.04 43.8 ± 11.6 91.4 ± 13.1............................................................................................................................................................................................................................................................................................................................................
Confidence Hills 2.02 ± 0.84 8.03 ± 2.11 20.8 ± 2.79 30.8 ± 3.60 29.3 ± 7.61 60.2 ± 8.42............................................................................................................................................................................................................................................................................................................................................
Confidence Hills blank 0.49 ± 0.18 3.04 ± 0.86 5.35 ± 0.83 8.88 ± 1.21 1.49 ± 0.42 10.4 ± 1.28............................................................................................................................................................................................................................................................................................................................................
RESEARCH | REPORT
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6. Organic matter preserved in 3-billion-year-old mudstones at Gale crater, Mars
Buch and Patrice Coll
Joel A. Hurowitz, John P. Grotzinger, Sanjeev Gupta, Doug W. Ming, Dawn Y. Sumner, Cyril Szopa, Charles Malespin, Arnaud
Brad Sutter, Amy C. McAdam, Heather B. Franz, Daniel P. Glavin, Paul D. Archer Jr., Paul R. Mahaffy, Pamela G. Conrad,
Jennifer L. Eigenbrode, Roger E. Summons, Andrew Steele, Caroline Freissinet, Maëva Millan, Rafael Navarro-González,
DOI: 10.1126/science.aas9185
(6393), 1096-1101.360Science
, this issue p. 1096, p. 1093; see also p. 1068Science
The seasonal variation provides an important clue for determining the origin of martian methane.
measurements of methane covering 3 martian years and found that the background level varies with the local seasons.
report atmosphericet al.numerous abiotic processes have been proposed to explain martian methane. Webster
of organic-rich sedimentary rock found on Earth. Most methane on Earth is produced by biological sources, but
preserved in 3-billion-year-old sediments. Heating the sediments released an array of organics and volatiles reminiscent
used two instruments in the SAM (Sample Analysis at Mars) suite to catch traces of complex organicset al.Eigenbrode
The Curiosity rover has been sampling on Mars for the past 5 years (see the Perspective by ten Kate).
Measuring martian organics and methane
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RELATED
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REFERENCES
http://science.sciencemag.org/content/360/6393/1096#BIBL
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